It is very difficult in a silver halide photographic light-sensitive material to satisfy both requirements of high sensitivity and excellent graininess. Therefore, the simultaneous satisfaction of both requirements has been an important theme in this art. For instance, although imparting high sensitivity to a silver halide photographic material can be achieved by increasing the size of silver halide grains, its graininess is greatly impaired if it is left intact without adopting any proper measures. Accordingly, with color photographic light-sensitive materials containing coarse-grained silver halide emulsions, the graininess has so far been improved by using particular couplers. As one of the measures, there has been the combined use of coarse-grained silver halide emulsions with so-called DIR couplers described in U.S. Pat. No. 3,227,554 or DIR compounds described in U.S. Pat. No. 3,632,435. Such DIR couplers and DIR compounds have a function to reduce clouds of the dye. Accordingly, the graininess is expected to be improved. However, such a measure decrease the sensitivity due to inhibitors released upon development and, does not improve the graininess in high density areas.
As another measure, an improvement in the graininess using diffusibility of dyes to be produced has been attempted in Japanese patent application (OPI) No. 82837/82 and so on. The so-called R.M.S. granularity (which is described in T. H. James, Theory of the Photographic Process, 4th Ed., p. 619) is greatly improved by using non-diffusing couplers capable of producing diffusing dyes which are moderate in smearing (which are simply called "diffusing dye-forming couplers" hereinafter). However, in middle and high density areas smears of dye, which each is formed in the periphery of developed spot through diffusion of dye molecules, adjacent to one another come to mingle therewith to form great overlaps of dye clouds and consequently, results in random formation of huge dye clouds since the arrangement of silver halide grains and the probability of development obey the random process. This phenomenon is visually quite disagreeable, and the graininess makes a rather bad appearance in the middle and high density areas, as the case may be.
That is, on the occasion that diffusing dye-forming couplers are employed, individual dye clouds come to have a low population density of dye and a large area as the result of dye molecules' diffusing in all direction with the same concentration inside the dye cloud (which are named "a dye cloud of diffusion type" hereinafter). Therefore, if graininess is expressed in the form of the so-called R.M.S. value, an improved value is derived. However, in areas of middle or higher densities large mottles formed by several dye clouds' gathering attract our attention and therefore, we get the impression that the graininess is visually poor. On the other hand, if the graininess is expressed in the form of Wiener spectrum (for detail of which T. H. James, The Theory of Photographic Process, 4th Ed., p. 621 should be referred to), diffusing dye-forming couplers are employed only to increase values corresponding to the low spatial frequency portion of the Wiener spectrum. (Such a value means better graininess the lower it is.) In practice also, though the graininess expressed in a form of R.M.S. value is improved by the use of diffusing dye-forming couplers, the resulting dye image assumes a quite disagreeable aspect and creates the impression that the graininess is deteriorated.